A method and apparatus for determining the switching states of a target wheel used in an internal combustion engine, the method including providing a camshaft, providing a target wheel having teeth coupled to the camshaft, providing a sensor to detect the teeth of the target wheel, providing a cam phaser to phase the camshaft relative to a crankshaft of the internal combustion engine, homing the cam phaser to a known position relative to the crankshaft, rotating the crankshaft and camshaft, detecting the switching of the teeth by the sensor, referencing switching information detected by the teeth to crankshaft position information to produce a calibration for the target wheel, and storing the calibration in a controller to be use for control of the internal combustion engine.
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9. A method of determining the switching states of a target wheel used in an internal combustion engine, the method comprising:
positioning a camshaft coupled to the target wheel to a home position using a cam phaser, said target wheel including a plurality of teeth; determining a crankshaft position relative to said home position; rotating said crankshaft and camshaft; sensing the target wheel teeth using a sensor to generate a pulse train; referencing said generated pulsetrain to said crankshaft position to generate a calibration, said calibration providing information on relative position between said camshaft and said crankshaft; and storing said calibration in a controller, said controller using said calibration to control the internal combustion engine.
1. A method of determining the switching states of a target wheel used in an internal combustion engine, the method comprising:
providing a camshaft; providing a target wheel having teeth coupled to said camshaft; providing a sensor to detect said teeth of said target wheel; providing a cam phaser to phase said camshaft relative to a crankshaft of the internal combustion engine; homing said cam phaser to a known position relative to said crankshaft; rotating said crankshaft and camshaft; detecting the switching of a plurality of said teeth using said sensor; referencing switching information detected by said plurality of teeth to crankshaft position information to produce a calibration for said target wheel; and storing said calibration in a controller to be used for control of the internal combustion engine.
5. A internal combustion engine comprising:
an intake manifold for providing air to the internal combustion engine; a throttle plate controlling the flow of said air; a fuel injector introducing fuel into said air to form an air/fuel mixture; at least one piston for combusting said air/fuel mixture; a plurality of valves to control intake and exhaust of said at least one piston; a first camshaft having a plurality of lobes to actuate said exhaust valves; a sprocket coupled to said first camshaft to drive said first camshaft; a crankshaft coupled to said sprocket via a timing belt; a cam phaser coupled to said first camshaft; a controller for controlling the position of said cam phaser; a target wheel coupled to said camshaft, said target wheel having teeth; and wherein said controller will command said cam phaser to rotate said camshaft to a home position referenced to said crankshaft position; and wherein said crankshaft is rotated to determine the switching positions of said teeth relative to said crankshaft position, said switching positions stored in said controller to control the position of said camshaft.
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The present invention relates to the control of an internal combustion engine. More specifically, the present invention relates to calibrating target wheels for speed, timing, and position sensing systems used in internal combustion engines.
Presently, automotive companies manufacture data or target wheels for use with speed sensors to detect the speed, timing, and position of an engine crankshaft and/or a camshaft. As is known in the art of four-cycle internal combustion engines (ICEs), position and timing between a crankshaft and a camshaft is very important for the application and synchronization of spark and fuel, as the camshaft actuates the intake and exhaust valves of an ICE. A camshaft may be used in an overhead valve (OHV) configuration where the valves are actuated via pushrods, or in an overhead cam (OHC) configuration where the valves are acted on directly by the camshaft. The camshaft is driven by the crankshaft through a 1:2 reduction (i.e., two rotations of the crankshaft equal one rotation of the camshaft) and the camshaft speed is one-half that of the crankshaft. The crankshaft and camshaft position, for engine control purposes, are measured at a small number of fixed points, and the number of such measurements may be determined by the number of cylinders in the ICE.
As previously described, engine control systems use the timing and position information supplied by a crankshaft and camshaft sensor for controlling the application of spark and fuel to the cylinders of an ICE. The position and timing (phase) of a first camshaft controlling exhaust valves for a cylinder and/or a second camshaft controlling intake valves for a cylinder in an overhead cam engine may be controlled relative to the crankshaft (piston position) to reduce emissions and improve fuel economy. Several cam-phasing devices (cam phasers) exist in today's automotive market that require accurate position and timing information provided by the camshaft position sensor. The crankshaft and/or camshaft position sensor typically include a variable reluctance or Hall effect sensor positioned to sense the passage of a tooth, tab and/or slot on a target or data wheel coupled to the camshaft.
The target or data wheel used with present camshaft position sensors have a distribution of teeth, tabs and/or slots. The camshaft position sensor typically comprises a variable reluctance or Hall effect sensor positioned to sense the teeth on a target or data wheel coupled to the camshaft. The magnetic properties and material composition of the target wheel will vary where and when the sensor senses the teeth on a moving target wheel. This variation may cause problems in the feedback provided by the sensor. For example, two target wheels with identical footprints but made of different materials will have different magnetic and switching characteristics. Referring to
The present invention comprises a target wheel calibration method and apparatus used to detect camshaft and crankshaft timing, position and speed for a four-cycle internal combustion engine ("ICE'"). The present invention utilizes a method of detecting the position of a target wheel tooth (or teeth) at a known position relative to the crankshaft and camshaft. The method comprises zeroing/homing a cam phaser coupled to the target wheel and camshaft and then rotating the crankshaft through two revolutions (thereby rotating the camshaft one revolution) to determine where the teeth of the target wheel switch the sensor. The switching time and position of the teeth of the target wheel on the camshaft are referenced to the target wheel pulse train of the crankshaft. The switching position of the target wheel on the camshaft is thus "known" with respect to the position of the crankshaft and corresponding cylinder events. This position and timing information is stored and referenced by a controller to control the functions of the ICE.
The various advantages of the present invention will become apparent to one skilled in the art upon reading the following specification and by reference to the drawings in which:
Referring to
The vehicle controller 22 may be any known microprocessor or controller used in the art of engine control. In the preferred embodiment, the controller 22 is a microprocessor, having nonvolatile memory NVM 26 such as ROM, EEPROM, or flash memory, random access memory RAM 28, and a central processing unit (CPU) 24. The CPU 24 executes a series of programs to read, condition, and store inputs from vehicle sensors. The controller 22 uses various sensor inputs to control the application of fuel and spark to each cylinder through conventional spark and fuel injector signals 30. The controller 22 further includes calibration constants and software stored in NVM 26 that may be applied to control numerous engine types.
In the preferred embodiment of the present invention, the ICE is equipped with an exhaust camshaft 14 and intake camshaft 19. The exhaust camshaft 14 and intake camshaft 19 are coupled to the crankshaft 12 via a timing belt or chain 25 and sprockets coupled to the camshafts 14, 19. The exhaust camshaft 14 actuates exhaust valves for the cylinders, and the intake camshaft 19 actuates intake valves for the cylinders, as is commonly known in the art. A target wheel 23 coupled to the exhaust camshaft 14 generates periodic signals using wheel speed sensor 18 to provide speed and position information for the exhaust camshaft 14. The wheel speed sensor 18 may be similar in functionality to wheel speed sensor 16.
The present invention may further be equipped with a continuously variable cam phaser 32, as is known in the art. The cam phaser 32 in the preferred embodiment is coupled to the exhaust camshaft 14. In alternate embodiments of the present invention, a cam phaser may be coupled to the intake camshaft 19 or to both the exhaust and intake camshafts 14, 19, or a common intake/exhaust cam depending on the desired performance and emission requirements of the ICE 10. The cam phaser 32 is preferably hydraulically modulated to create a variable rotational offset between the exhaust camshaft 14 and the intake camshaft 19 and/or the crankshaft 12. The degree of rotational offset generated by the cam phaser 32 enables the ICE 10 to be tuned for specific performance requirements by varying valve overlap, i.e., overlap between the exhaust and intake valves of the ICE 10. In applications where it is required that NOx components are reduced, the cam phaser 32 can provide charge dilution in the form of recirculated exhaust gases. Charge dilution is a method of adding an inert substance to the air/fuel mixture in a cylinder of the ICE 10. The inert substance will increase the heat capacity of the air/fuel mixture and reduce the amount of NOx components created during combustion. Accordingly, by regulating the valve overlap area, NOx components may also be regulated. Furthermore, engine performance characteristics such as horsepower and fuel economy may also be modified using the cam phaser. For an ICE equipped with camshafts that operate both intake and exhaust valves, valve timing relative to the combustion cycle may be adjusted.
Referring to
Referring to
In the preferred embodiment of the present invention, the pulse train 52 has been processed to provide a specific cylinder event for each specific pulse. For example, a six pulse period for pulse train 52 will correspond to a six cylinder engine, each pulse indicating the top dead center (TDC) or bottom dead center (BDC) position for the six cylinders. Referring to
Where C=the crankshaft-to-camshaft exhaust camshaft angle
D=the crankshaft period in degrees
E=the period between cylinder and cam events
F=the period between cylinder events
Where D=(720 degrees)/(the number of cylinders in the engine)
The method of the present invention can be described as first zeroing or homing the cam phaser 32 coupled to the target wheel 23 and then rotating the target wheel 23 one revolution such that teeth 40/41 generate the pulse train 54. The individual pulses generated by the teeth 40/41 are referenced to pulses/cylinder events generated by the crankshaft 12 in the pulse train 52 and stored in the controller 22. All camshaft 14 phase positions are thus referenced individually relative to the home position and cylinder events in the pulse train 52. The position of the crankshaft 12 is known to be a certain number of counts from the void 46. Accordingly, by zeroing the cam phaser 32 and learning the individual positions of the teeth 40/41 on startup, the sensor 18 (and sensor 16) will be able to reproduce a consistent signal from teeth 40/41 of target wheel 23. Thus, the physical cam position relative to crank or cam phase may be determined while simultaneously negating effects of tooth to tooth variation on the calculation of the cam phase angle.
The preferred method of the present invention can be seen in
While this invention has been described in terms of some specific embodiments, it will be appreciated that other forms can readily be adapted by one skilled in the art. Accordingly, the scope of this invention is to be considered limited only by the following claims.
Davis, Jason Thomas, Mathews, David Stewart, Warner, Donald Clayton
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